1. Field of the Invention
The present invention relates to a fuel injection valve which injects fuel into a combustion chamber of an internal combustion engine or the like.
2. Description of Related Art
An internal combustion engine has a fuel injection valve for injecting fuel into each of a plurality of combustion chambers. This injection valve has a valve guide formed in a cylindrical shape and a valve member. The valve guide has nozzle holes. The valve member is disposed in a center opening of the guide. The valve member is reciprocated to be seated on a valve seat of the guide and to leave the seat. Therefore, the holes are repeatedly opened and closed. A fuel passage is formed between the valve guide and the valve member. When the valve member leaves the seat, fuel flows through the fuel passage and is injected into the chamber through the holes.
Because each hole is formed in a small size, a portion of the fuel injected through the hole easily remains as residues on a surface of the valve guide placed around fuel outlets of the holes. These fuel residues are exposed to combustion products (e.g., CO2, CO, H2O, NO, and the like) having high temperatures during the operation of the engine. Further, when the operation of the engine is stopped, the residues are cooled down. Therefore, the residues are solidified or caked as deposits on the valve guide around the fuel outlets of the holes. These deposits placed around the holes change the spray angle of the injected fuel and/or the shape of the spray formed by the injected fuel. In this case, it is difficult to maintain the fuel injection performance of the injection valve at a superior level.
To solve this problem, Published Japanese Patent First Publication No. 2001-90638 discloses a fuel injection valve wherein an organic layer made of perfluoropolyether compound such as FAS (fluoro-alkyl-silane) or the like is attached to the surface of a valve guide around nozzle holes of the guide. FAS has water repellency. The FAS layer prevents fuel from being attached to the surface of the valve guide as deposits, or the deposits attached to the surface of the valve guide are easily detached due to the FAS layer.
However, this injection valve in the Publication No. 2001-90638 has the problem that FAS thermally decomposed is attached to the surface of the valve guide More specifically, a portion of the valve guide on the downstream side of the holes is heated by combustion products. Therefore, FAS attached to the surface of the valve guide is thermally decomposed and reacts with P, Zn, Si, compounds of carboxylic acids and base components, and the like contained in the fuel to produce low melting amorphous glass. Therefore, PAS thermally decomposed has no water repellent performance. Further, the low melting amorphous glass derived from thermally decomposed FAS and fuel residues containing non-burned carbon forms deposits, and these deposits become fixed and attached to the surface of the valve guide around the holes.